It Is The Heat

Phoenix just provided another reason to hate flying: the heat.  With temperatures there expected to hit 119 degrees Fahrenheit, airlines canceled more than 40 flights today. ...  The heat poses a particular problem for the Bombardier CRJ airliners, which have a maximum operating temperature of 118 degrees. 

-- Rhett Allain, Wired Magazine, "Why Phoenix's Airplanes Can't Take Off in Extreme Heat", 20 June 2017